1. Field of the Invention
The present invention relates to an antenna element and a communication apparatus provided with the same, and more specifically, to an antenna element capable of being adapted to a plurality of frequency bands and a communication apparatus provided with the same.
2. Description of the Related Art
In related art, in a communication apparatus such as a mobile computer apparatus having a communication function and a mobile communication terminal, in order to respond to diversification of uses and functions thereof, various antenna elements have been proposed which are capable of being adapted to a plurality of frequency bands (see, for example, Japanese Patent Application Laid-open Nos. 2006-196994 and 2008-177668 (hereinafter, referred to as Patent Documents 1 and 2, respectively)).
FIG. 15 is a diagram showing the structure of an antenna element proposed in Patent Document 1. An antenna element 200 disclosed in Patent Document 1 is constituted of a first antenna element 201 of a folded monopole type and a second antenna element 202 of an end open type.
In the first antenna element 201 disclosed in Patent Document 1, the total length of an outward way from a feeding point 203 to a folded point and a return way from the folded point to a ground point 204 is set to a ½ wavelength of a first resonant frequency. Further, in the second antenna element 202, the length from the feeding point 203 to an open end via a branch point 205 is set to approximately ¼ wavelength of a second resonant frequency. Furthermore, in the antenna element 200 disclosed in Patent Document 1, the total length of the return way from the feeding point 203 to the ground point 204 via the branch point 205 and a short-circuit unit 206 is set to approximately ½ wavelength of the second resonant frequency, and the path portion is caused to function as a stab of the second antenna element.
In Patent Document 1, the antenna element 200 is configured as described above, thereby simplifying the shape of the antenna element 200 capable of causing multiple resonances and making an impedance adjustment, with the result that the antenna element is easily built in a radio apparatus.
FIG. 16 is a diagram showing the structure of an antenna element disclosed in Patent Document 2. An antenna element 210 disclosed in Patent document 2 is constituted of a feeding-side part element 211, a folded part element 212, and end open part element 213. The feeding part element 211 has a predetermined width d, and is formed to be extended from a feeding point 211a on a substrate 207 toward a first branch point 211b. The folded part element 212 branches from the feeding-side part element 211 at the first branch point 211b, is folded at the folded part 212a, and is thereafter grounded at a ground end 212b on the substrate 207. Further, the end open part element 213 branches from the feeding-side part element 211 at a second branch point 211c, and the end thereof is an open end 213a. Further, an outward way and a return way of the folded part element 212 are short-circuited at a short circuit point 212c on the way.
In Patent Document 2, the antenna element 210 is configured as described above, with the result that the multiple resonances of the antenna element and the reduction in size and height thereof are realized at the same time, and the independence of the impedance adjustment in different resonant frequencies is realized.
Further, as an antenna element capable of being adapted to a plurality of frequency bands, other than the antenna elements disclosed in Patent Documents 1 and 2, for example, an antenna element has been proposed which uses two inverted-F antennas in which a feeding unit and a short-circuit unit thereof are shared. FIG. 17 shows a structural example thereof. It should be noted that FIG. 17 shows the structure of an antenna element 220 capable of being adapted to two frequency bands.
The antenna element 220 shown in FIG. 17 is constituted of a dielectric portion 7, a low-frequency band antenna main body unit 1, a high-frequency band antenna main body unit 2, a feeding unit 3, and a short-circuit unit 224. The dielectric portion 7 is provided on a substrate 20. The low-frequency band antenna main body unit 1 contributes to a response to a radio signal in a low-frequency band. The high-frequency band antenna main body unit 2 contributes to a response to a radio signal in a high-frequency band.
The low-frequency band antenna main body unit 1 and the high-frequency band antenna main body unit 2 each are formed of a line path. Further, the low-frequency band antenna main body unit 1 and the high-frequency band antenna main body unit 2 are integrally formed on the dielectric portion 7. Specifically, one end portion of the low-frequency band antenna main body unit 1 in an extended direction and one end portion of the high-frequency band antenna main body unit 2 in an extended direction are connected to each other. It should be noted that another end portion 1a of the low-frequency band antenna main body unit 1 and another end portion 2a of the high-frequency band antenna main body unit 2 are open ends. In the antenna element 220 shown in FIG. 17, between the substrate 20 and a connection point 1b (hereinafter, referred to as branch point 1b) of the low-frequency band antenna main body unit 1 and the high-frequency band antenna main body unit 2, the feeding unit 3 and the short-circuit unit 224 are formed in parallel.
That is, the antenna element 220 shown in FIG. 17 has two open ends, one feeding point, and one ground point, unlike the antenna elements (each having one open end, one feeding point, and one ground point) disclosed in Patent Documents 1 and 2.